well, we're moving right along. last week i did clefs, importing measures (exporting had been done a while back) and notes of varying duration. I made an executive decision on that last one not to support importing chords with notes of more than one duration - something that's not really supported in Gsharp. While nothing in MusicXML stops you from doing it, it's not usually the best notational style; if the notes have different durations, they should probably be notated as being in separate voices.
I capped it off over the weekend by doing rests. Had a brief moment of trying to leverage CL's method combinations to export rests, since both they and clusters are melody-elements with the same interface for rhythmic properties and whatnot. I decided not to do it, because the nature of the whole thing seemed to make it more trouble than it was worth.